1. Field of the Invention
The invention relates to power circuit protection and control device simulators. One embodiment of the present invention enables a user to simulate actual operation of a motor overload relay and electric motor, via a web browser, using at least some of the identical control parameters of the manufactured relay product. The simulator of the present invention is useful for training users in the operation of a control device and testing simulated operation in a non-destructive virtual environment, without risk of physical damage to actual power equipment. By way of example, a user can test intermittent operation of a simulated motor and overload relay under varying load test conditions envisioned in a future factory design, to determine whether the overload relay will trip due to simulated motor thermal overload, without having to configure an actual motor test bed. The simulator of the present invention also allows non-destructive virtual testing of new control functions, such as new thermal modeling protection algorithms prior to bench testing.
2. Description of the Prior Art
Electrical distribution and power circuit designers, engineers, maintenance technicians, equipment specification/purchasing managers and others in the field need to understand the features, functions and operational characteristics of residential, commercial and industrial electrical equipment. Given the complexities of modern electrical equipment components and electrical distribution system design environments, it is desirable to understand, prior to actual construction, how equipment will interoperate once connected to a working system.
In the past, longer construction lead times and relatively fewer variations of relatively simpler electrical equipment allowed designers to use best professional judgment and experience to design and specify electrical distribution systems. In due course, the system would be built and “de-bugged” as necessary in the field in order to achieve acceptable operational performance. Present shorter design and construction lead times, greater variation and complexity of equipment, and high repair and replacement cost of electrical equipment have created demand for pre-construction system performance verification.
One common electrical power system application in industrial and commercial environments is an electrical motor powering an intermittent, varying load. A motor overload relay is interposed between an electrical power source and the motor in order to protect the motor from overload conditions, such as a stalled or locked rotor, and overheating from excessive or rapid intermittent loads that do not allow the motor to cool sufficiently. The overload relay is sized, through equipment performance specification, control settings (i.e., maximum rated steady-state operational, maximum in-rush current during startup, permissible phase unbalance variations, etc.) and empirical testing, to protect the motor from overheating, yet avoid inadvertent nuisance tripping.
In the past, through professional judgment, experience and trial and error, an electrical system designer would attempt to match a motor and overload relay combination to be able to conform to the anticipated system design operational requirements. The designer could consult product specification sheets, time vs. current heat charts and the like to specify a particular rating and adjustment settings of a motor overload relay. Product specification, testing and configuration were heavily dependent upon the empirical experience of the designer. Upon actual construction, the combination would be tested and verified in the field. If the system overheated or was subject to nuisance tripping, different overload relay control adjustment settings would be tested. If performance remained unsatisfactory a different specification overload relay might be needed to replace the one in the initial design.
The time-consuming trial and error specification methodologies and development of designer professional experience had to be passed on to designer trainees. Need has long existed in the electrical system design arts to provide simulation training tools that would enable experienced design professionals to configure system designs in quicker fashion with minimal design corrections and to provide training experience for less experienced design trainees.
In the past there have been attempts to make electrical distribution circuit protection simulation apparatus that would enable a designer to mimic loads on multiple circuit breakers in a distribution system, so that faults could be isolated to the circuit breaker most closely associated with the fault node. Such systems essentially allowed computer-stored time/current charts to be overlayed, so that the correct circuit breaker size could be verified, as well as overload current settings (e.g., ground fault, instantaneous trip and other time/current settings). Time/current data were generally gathered empirically. For example, for a specific design and load capacity of an electric motor, acceptable performance time/current charts were derived so that motor heat capacitance operational limits were understood by designers. Generally such charts were created with conservative operational parameters, so as to minimize risk of motor damage.
As motor control electronics became more sophisticated, microprocessor-controlled overload relays were developed that could digitally model electrical motor heat capacitance and heat transfer in real time. An example of such motor controllers is described in U.S. Pat. No. 5,539,601, “Apparatus and Method for Thermal Protection of Electric Motors”. Motor temperature overload control algorithms described in the patent allowed for more precise, real time evaluation of motor heat capacitance and heat transfer. Rather than select conservative control settings based on imperfect empirical data, the motor controller could more successfully model actual motor operating conditions, and if necessary cause a motor contactor to de-energize power to the motor before the motor became overheated. However, motor controllers of the type shown in U.S. Pat. No. 5,539,601 were intended for field application and not as virtual simulator test beds. Both the control algorithms and control settings had to be bench or field tested. It is desirable to confirm operability of control algorithms and control settings prior to bench testing or field installation.
Thus, a need exists in the art for an electrical power distribution system circuit protection and control simulator that enables designers to test and verify system designs and equipment configuration virtually. A need also exists in the art for an electrical power distribution system circuit protection and control simulator that enables design and maintenance professionals to learn about the interoperability, compatibility and operational characteristics of components in a “hands on” virtual environment.